We identified PAI-1 as a major factor that turns radiosensitive cells into radioresistant cells in a paracrine manner, via a cell-extrinsic action that enhances the proliferation of recipient PAI-1-negative/low NSCLC cells through PAI-1-mediated AKT and ERK1/2 activation. The gene discussed is MAPK3; the disease is non-small cell lung carcinoma.